Germanium, an optical material, has high transmittance and refractive index and low light scattering in the infrared region, and research is being conducted to utilize it in various industrial fields. Various forms of optical lenses can be subjected to ultra-precision machining with high quality surface roughness, and they form accuracy through single point diamond turning (SPDT). In particular, the diamond tool with a negative rake angle and the u-LAM process that applies a 1,064 nm laser to the material have been studied to fabricate brittle materials into optical lenses. In this study, the effects of process parameters, such as laser power (W), spindle speed (RPM), feed rate (mm/min), and depth of cut (μm), on the surface roughness of a sub-nanometer scale and the occurrence of defects during the machining process were analyzed for Germanium materials. The process of removing these defects was also analyzed.

Recently the interest in miniaturization of mechanical devices has increased and magneto-rheological (MR) fluid brakes have been designed, fabricated and tested to be applied as a control element of various devices for assisting the elderly people. A multi-disk modular type of design is proposed to make an MR fluid brake that can generate high torque at the minimum size. The design parameters of the MR fluid brake were determined by mathematical modeling and the performance was predicted with magnetic analysis to maximize the design torque. A testbed was constructed and torque responses were measured and analyzed according to the input current for various rotational speeds to confirm the performance of the MR fluid brake. The experimental results showed that the MR fluid brake was applicable to actuating devices for assisting elderly people.